Multi axial Fatigue Analysis not displaying the dynamic area results

[Anonymous]

Hello everyone,

I'm performing the multi.-axial fatigue analysis for a shaft. I've at least 9 different forces that are acting on the component. So after running the analysis, it is supposed to show the results due to each individual force before the fatigue results.

But unfortunately, I'm seeing only one result with only one among the applied forces considered. I'm unfortunately not sure if I had missed any settings and since I'm not seeing the results due the individual force, I'm unsure whether In-CAD has actually taken all the forces into consideration for the fatigue results.

I'm suing Nastran-InCAD Version 2019.2.0.288 and Autodesk Nastran 13.2.0.168

Thanks and Regards,

Prasanna. 

[John_Holtz]

Hi @Anonymous 

I am investigating whether the change in 2019 Nastran was intentional or not. For example, it could be that the results of the single subcase are the results from all of the applied loads. Can you determine if that is true from the results? For example, is the SPC Summation result for the constraints equal to the entire load?

Also, can you clarify what is shown in your two images? How, what version, or at what stage were the two images created?

[John_Holtz · Accepted solution]

Hi,

I have discovered that the 2019 version of Nastran does not handle multiple loads correctly in a Multiaxial Fatigue analysis. If is only outputting one set of stress/displacement results because it is only analyzing one of the loads. The other loads are not used in the analysis. (Therefore, my guess that the analysis was including all of the loads was incorrect.)

This problem has been fixed in version 2020, so that would be one solution. Version 2018.2 did not have the issue, so using a previous version of Nastran would be another solution.

[Anonymous]

Hello @John_Holtz ,

thanks for the information and sorry for the late reply. I performed the results once again with Nastran 2018.2 and was able to get the results with individual forces again.

But I have one question about that. By saying that Nastran 2019 has a problem with multiple loads, does the end fatigue results are with only one load or all the loads given in the load cases?

Thanks and Regards,

Prasanna

[John_Holtz]

Hi @Anonymous 

That is a good question.

The fatigue results are wrong because they are based on only one of the applied loads. The fatigue results are not based on all of the applied loads.

I had written an article to describe this problem, but your question was not clearly answered in it. I will revise the article to make it more clear that the results are incorrect. (See Multi-axial fatigue analysis with multiple loads not displaying multiple results in Nastran.)